1. Field of the Invention
This invention relates to mechanisms for opening and closing doors, and more particularly, to a door operator system which uses an actuator with a relatively short stroke length to move the door over a distance that is longer than the actuator stroke length.
2. Description of the Related Art
Many door operator systems over the years have been developed to assist persons in opening and closing doors from a remote location. Such systems typically include an electric motor mounted to a wall or ceiling of a garage or other structure. A sprocket is mounted to the motor shaft, or the shaft of a gear reduction assembly associated with the motor. A continuous chain is looped over the sprocket and one or more links of the chain are typically connected to the door through an arm member. Rotational movement of the motor thus causes opening or closing movement of the door.
Instead of the sprocket and chain assembly, the electric motor may be associated with a power screw assembly for opening and closing doors. U.S. Pat. No. 4,075,952 issued to Burge on Feb. 28, 1978 discloses a scissor-type slide gate opener for railroad cars. The opener has a cylindrical shaft with right and left-handed threads. Links are mounted to the shaft at pivot points and move axially along the shaft during rotation of the shaft. First arms are pivotally mounted to a stationary frame member and include gears that intermesh, and a pair of sockets that engage a pair of blocks. Second arms are pivotally connected between the first arms and a gate. Rotational movement of the shaft causes rotation of the first arms, which in turn causes sliding movement of the gate.
Other door operator systems include pneumatic assemblies, such as U.S. Pat. No. 4,891,908 issued to Aquilina on Jan. 9, 1990; or a combination of pneumatic and chain assemblies, as disclosed in U.S. Pat. No. 4,417,418 issued to Warning on Nov. 29, 1993.
The length of chains, power screws, air cylinders, etc. of prior art door operators are typically equal to or greater the distance needed to move the door between open and closed positions. Consequently, such operators can be unwieldy, difficult to install, and high in cost.